System and methods for tissue mapping and ablation

ABSTRACT

A steerable electrophysiology catheter includes a shaft having a distal ablation segment with one or more electrodes coupled to a source of electrical energy by a connector extending through the shaft. The distal ablation segment of the shaft is movable between a collapsed configuration sized for percutaneous introduction into the patient and/or endoluminal delivery to the target site and an expanded configuration, in which the distal ablation segment forms a substantially continuous surface transverse to the shaft axis for engaging the heart tissue and creating a linear lesion thereon. The catheter includes one or more force element(s) positioned to apply an axial force between the distal and proximal ends of the ablation segment. The force element(s) provide a sufficiently uniform force against the distal ablation segment to establish continuous contact pressure between the electrodes and the patient&#39;s heart tissue. This contact pressure allows the surgeon to engage the entire length of the distal ablation segment against the heart tissue to provide a relatively long linear lesion on this tissue.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of patent application Ser.No. 08/794,804 filed Feb. 4, 1997, now U.S. Pat. No. 5,916,213. Thisapplication is also related to commonly assigned patent application Ser.No. 08/794,066 entitled "Linear Ablation Catheter", now U.S. Pat. No.5,919,188, and patent application Ser. No. 08/794,803 entitled "FluidCooled Ablation Catheter and Method for Making", now U.S. Pat. No.5,913,854. The complete disclosure of any and all patents, patentapplications and printed publications referred to herein areincorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to systems and methods forapplying electrical energy to a patient and more specifically tosteerable electrophysiology catheters for use in mapping and/or ablationof the heart.

The heart is primarily composed of multiple fibers which are responsiblefor the propagation of signals necessary for normal, electrical andmechanical function. The presence of an arrhythmogenic site or abnormalpathway which may bypass or short circuit the normal conducting fibersin the heart often causes abnormally rapid rhythms of the heart, whichare referred to as tachycardias. Tachycardias may be defined asventricular tachycardias (VTs) and supraventricular tachycardias (SVTs).VTs originate in the left or right ventricle and are typically caused byarrhythmogenic sites associated with ventricular myocardial disease.SVTs originate in the atria or the atrioventricular (AV) junction andare frequently caused by abnormal circuits or foci.

The present invention is concerned with the treatment of atrialfibrillation and atrial flutter, which are two of the most commonsustained cardiac arrhythmias and of the major causes of systemicembolism. Therapy for patients suffering from atrial fibrillationusually focuses on controlling the symptoms (palpitations, angina,dyspnea, syncope and the like), improving cardiac performance andreducing the risk of thromboembolism. Treatment of atrial fibrillationmay be accomplished by a variety of approaches, including drugs,surgery, implantable pacemakers/defibrillators, and catheter ablation.While antiarrhythmic drugs may be the treatment of choice for manypatients, these drugs may only mask the symptoms and do not cure theunderlying cause. Implantable devices, on the other hand, usually cancorrect an arrhythmia only after it occurs. Surgical and catheter-basedtreatments, by contrast, may actually cure the problem usually byablating the abnormal arrhythmogenic tissue or abnormal pathwayresponsible for the atrial fibrillation or flutter. The catheter-basedtreatments rely on the application of various destructive energy sourcesto the target tissue including direct current electrical energy,radiofrequency electrical energy, microwave energy laser energy,cryoenergy, ultrasound and the like.

Of particular interest to the present invention are radiofrequency (RF)ablation protocols which have proven to be effective in treatment ofatrial fibrillation while exposing the patient to minimum side effectsand risks. Radiofrequency catheter ablation may be performed after aninitial mapping procedure where the locations of the arrhythmogenicsites and abnormal pathways are determined. A catheter having a suitableelectrode is introduced to the appropriate heart chamber and manipulatedso that the electrode lies proximate the target tissue. Radiofrequencyenergy is then applied through the electrode to the cardiac tissue toablate a region of the tissue which forms part of the arrhythmogenicsite or the abnormal pathway. By successfully destroying that tissue,the abnormal conducting patterns responsible for the atrial fibrillationor flutter cannot be sustained. Methods and systems for performing RFablation by controlling temperature at the ablation site are describedin co-pending application Ser. No. 07/866,683, now U.S. Pat. No.5,573,533 entitled "Method and System for Radiofrequency Ablation ofCardiac Tissue," filed Apr. 10, 1992, the complete disclosure of whichis hereby incorporated by reference.

Catheters designed for mapping and/or ablation frequently include anumber of individual electrode bands mounted to the distal tip of thecatheter so as to facilitate mapping of a wider area in less time, or toimprove access to target sites for ablation. Such catheters aredescribed in co-pending application Ser. No. 07/866,383, now U.S. Pat.No. 5,318,525 filed Apr. 10, 1992, the complete disclosure of which ishereby incorporated by reference. Catheters utilized in radiofrequencyablation are typically inserted into a major vein or artery, usually inthe neck or groin area, and guided into the chambers of the heart byappropriate manipulation through the vein or artery. Such catheters mustfacilitate manipulation of the distal tip or ablation segment so thatthe distal electrode(s) can be positioned against the tissue region tobe ablated. The catheter must have a great deal of flexibility to followthe pathway of the major blood vessels into the heart, and the cathetermust permit user manipulation of the distal ablation segment even whenthe catheter is in a curved and twisted configuration. Because of thehigh degree of precision required for proper positioning of the tipelectrode, the catheter must allow manipulation with a high degree ofsensitivity and controllability.

An important factor which has driven the recent development of curativecatheter ablation therapies for atrial fibrillation has been thedevelopment of a successful surgical procedure, the "Maze" procedure,for treating patients with this arrhythmia. The Maze procedure wasdeveloped to provide both sinus node control of ventricular rate andeffective, appropriately synchronized biatrial contraction. Thisprocedure involves opening the patient's chest cavity with a grossthoracotomy, usually in the form of a median sternotomy, to gain accessinto the patient's thoracic cavity, and cutting long linear incisionsthrough the heart wall to electrically partition portions of the heart.In particular, the Maze procedure partitions the atria such that: (1) noportion of the atrium is large enough to support atrial fibrillation;(2) conduction of the sinus impulse to the AV node and to most portionsof the atria is maintained; and (3) relatively normal atrial contractionis restored.

The success of the Maze procedure has driven interest in the developmentof a catheter ablation procedure which can replicate the therapeuticresults of the surgical Maze procedure. This catheter ablation procedureinvolves the creation of relatively long linear lesions along the hearttissue with the distal tip of an ablation catheter. This desire toproduce linear lesions has led to catheter designs in which severalablation electrodes are mounted on the length of the distal ablationsegment of the catheter shaft. By engaging the entire length of thedistal ablation segment with the heart tissue, a string of "point"lesions are connected together to form a linear lesion. When contact ofthe distal ablation segment shaft is attempted with standard catheterdesigns, however, the line of force to the ablation segment is typicallyapplied from the proximal end, while the distal tip of the ablationsegment remains relatively free. Consequently, contact pressure of thedistal tip of such a catheter is dependent upon the relative stiffnessof the distal ablation segment, and the translation of force by theoperator through the main catheter shaft to the proximal portion of theablation segment. This inefficient application of force along the distalablation segment of the catheter results in non-uniform (and ofteninadequate) application of contact pressure at each point along thedistal ablation segment.

SUMMARY OF THE INVENTION

The present invention provides devices and methods for applyingelectrical energy to a patient. In particular, the invention provides asteerable electrophysiology catheter for mapping and/or ablation ofheart tissue during procedures such as atrial and ventriculartachycardias, particularly atrial fibrillation and flutter. The catheterof the present invention applies a centralized force to a distalablation segment, which more uniformly distributes across the distalablation segment to establish continuous contact pressure between theablation segment and the patient's heart tissue. This uniform continuouscontact pressure allows the operator to engage substantially the entirelength of the distal ablation segment against the heart tissue toprovide a relatively long, linear lesion on this tissue.

A steerable electrophysiology catheter according to the inventionincludes a shaft having distal and proximal ends and an ablation segmentat the distal end. One or more electrodes are spaced along the ablationsegment, and coupled to a source of energy by a connector extendingthrough the shaft. Energy sources may include direct current electricalenergy, radiofrequency electrical energy, microwave energy laser energy,cryoenergy, ultrasound and the like. Preferably, the energy source is aradiofrequency generator. The distal ablation segment is movable betweena collapsed configuration sized for percutaneous, intercostal and/orendoluminal delivery to the target site, and an expanded configuration,in which the distal ablation segment forms a substantially continuoussurface transverse to the shaft axis for engaging the heart tissue andforming a continuous lesion thereon. The catheter includes one or moreforce element(s) positioned to apply an axially directed force betweenopposite ends of the ablation segment. The force element(s) provide acentralized and substantially uniform axial force against the ablationsegment to increase the contact pressure between the electrodes spacedalong the ablation segment and the heart tissue. This increased contactpressure allows engagement of substantially the entire ablation segmentagainst the heart tissue so that a continuous linear lesion may beformed on the tissue.

Another advantage of the present invention is that the distal ablationsegment is preferably coupled to the catheter shaft by a substantiallyrigid hinge assembly. The hinge assembly allows the distal ablationsegment to pivot about the shaft into a suitable orientation transverse(i.e., angles from about 1-359 degrees relative to the shaft axis) tothe shaft axis for creating a linear lesion on the tissue. The rigidhinge assembly effectively secures the ablation segment in thistransverse orientation so that the surgeon can apply pressure againstthe ablation segment (either distal or proximally directed forces) tomaintain contact pressure between substantially the entire length of thesegment and the heart tissue.

In one embodiment, the distal ablation segment has a split-tipconfiguration comprising first and second arm segments pivotally coupledto a hinge assembly at the distal end of the catheter shaft. The armsare pivotable about the hinge assembly between a collapsedconfiguration, where the arm segments are folded together and generallyparallel to the shaft axis, and an expanded configuration, where thearms are split apart to form a continuous surface transverse to theshaft axis. Usually, the arms will define an angle between about 1 to270 degrees in the expanded position, preferably about 90 to 180 degreesand more preferably between about 120 to 175 degrees. This latterconfiguration causes a spring-like contact at the ends of the ablationarms to facilitate the application of axial force by the catheter shaftagainst the arms. Each arm segment includes a plurality of ablationelectrodes formed on an outer surface of the arm segments. Electricalconnectors extend from the electrodes, through the hinge assembly andthe catheter shaft, to a proximal connector for coupling the electrodesto a source of electrical energy, such as a Radiofrequency generator, orother suitable energy source.

In one aspect of the invention, the arm segments are substantiallycylindrical, and the electrodes are coils, rings, half-rings or balloonsextending around the cylindrical arms. In another aspect of theinvention, the arm segments have a semi-circular cross-section with asubstantially planar contact surface. Flattened coil electrodes ormetallic pads attached to underlying support plates or other suitableelectrodes are disposed on the planar contact surface. In this latterarrangement, the hinge assembly includes a pair of hinges that areoffset from the shaft axis and disposed adjacent each other to minimizeinterference with the tissue/electrode interface.

In yet another aspect of the invention, each arm segment also includes afluid channel for directing coolant therethrough to bathe the targetsite with fluid and/or convectively cool the electrodes. In an exemplaryembodiment, the fluid is an ionic solution, such as isotonic saline. Inthis configuration, the fluid is directed between the electrodes andtissue at the target site to complete the current path between theelectrodes and the tissue. The ionic solution effectively carries the RFablation energy to inhibit or prevent direct contact between theelectrodes and the tissue to minimize tissue damage and fluid (e.g.,blood) coagulation on the electrodes.

The force element(s) are preferably disposed between the arm segments atthe hinge assembly, and include a connector extending to the proximalend of the catheter shaft. Preferably, at least one of the forceelements is the catheter shaft, which can be manipulated to apply acentral, symmetric axial force against the arms at the hinge assembly inthe expanded position to effectively ensure that the arms maintainsufficient contact pressure against the heart tissue during the ablationprocedure. The force element(s) may also actuate the hinge assembly topivot the arm segments between the folded and expanded positions. In aspecification configuration, the force element(s) additionally includeone or more actuator wires extending through the catheter shaft from aproximal handle to the hinge assembly. The handle includes a user inputcontrol, such as a slide ring, knob, button or the like, for axiallytranslating the manipulator wires. This axial translation of theactuator wires causes the arm segments to pivot about the hingeassembly. The handle may include additional input controls for providingadditional degrees of freedom, such as rotation of the ablation segmentabout the catheter shaft, curvature of the catheter tip, and the like.

In another embodiment of the invention, the distal ablation segmentincludes a single, linear ablation segment coupled to the catheter shaftby a pair of curved, flexible support shafts. The curved support shaftsextend radially and distally outward from the catheter shaft to supportthe linear ablation segment at points between its ends and midspan. Theablation segment includes a central hinge structure and outer movableportions that pivot about the hinge structure. A centrally mounted pullwire within the catheter shaft causes the outer portions of the ablationsegment to collapse and expand at the central hinge pivot point. Theouter portions of the ablation segment preferably define an angle ofabout 120 to 170 degrees in the expanded configuration. The supportshafts, together with a central manipulator wire, function as the forceelements to apply a balanced axial force against the ablation segment inthe expanded configuration. Alternatively, the catheter shaft mayinclude a pair of flexible arms that extend distally away from eachother to form a Y-shaped arrangement at the distal end of the shaft. Inthis configuration, the arms are biased toward each other, and can bepivoted about a central "living" hinge to urge the arms into an expandedconfiguration.

In another embodiment of the invention, the distal ablation segment is asingle, continuous member that pivots around the distal end of thecatheter (rather than collapsing upon itself as in the previousembodiments). The distal portion of the catheter shaft preferablyincludes a cut-out or longitudinal opening for allowing the ablationsegment to pivot from a collapsed or generally parallel orientationwithin the longitudinal opening of the shaft to a deployed orientationtransverse to the shaft. The ablation segment may also be drawn proximalinto the shaft, if desired. The force elements in this embodimentpreferably include the catheter shaft and a pair of curved flexiblesupport shafts that extend from the distal end of the catheter shaft tosupport the ablation segment. One of the support shafts may also bedrawn proximally into the catheter to pivot the ablation segment aboutthe distal end of the catheter.

In a preferred aspect of a method of the present invention, an ablationsegment is positioned adjacent the target site on the patient's heart.The ablation segment may be introduced and delivered endoluminally tothe target site with a delivery catheter, it may be delivered through anintercostal penetration with a catheter or probe, or directly into thethoracic cavity through a thoracotomy. Once in position, the pullwire(s) are moved axially to pivot the arm segments (or rotate thesingle ablation segment) into the expanded position transverse to theshaft axis. The catheter can then be moved distally to engage the hearttissue at the target site. The actuator wires, catheter shaft and/orsupport shafts will exert an axial force against the distal ablationsegment to maintain sufficient contact pressure with the heart tissue sothat the electrodes create a linear lesion against this tissue. In anexemplary embodiment, the surgeon will create a number of linear lesionsin the heart tissue to electrically partition portions of the atria(i.e, similar to the Maze procedure).

Alternatively, if the electrodes were mounted circumferentially aroundthe arm segments, or on the "backside" of the arm segments, the cathetercould be pulled proximally to engage the heart tissue. For example, thecatheter may be pulled into a vessel to engage the heart tissuesurrounding the vessel opening, such as the ostium of a vein or arteryor a valve annulus, or against the septal wall of the left atriumthrough a transseptal puncture. Radiofrequency current could then bedelivered through a connector in the shaft and suitable electrode wiresto the electrodes on the ablation segment(s), through which current isconducted to the heart tissue to perform ablation.

Other features and advantages of the invention will appear from thefollowing description in which the preferred embodiment has been setforth in detail in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a steerable electrophysiology catheterconstructed in accordance with the principles of the present invention;

FIGS. 2A and 2B are side cross-sectional views of distal and proximalportions, respectively, of a deflectable tip of the catheter of FIG. 1;

FIGS. 2C-2E are transverse cross-sectional views taken along lines C--C,D--D, and E--E respectively, through the distal portion of thedeflectable tip of FIG. 2A;

FIGS. 2F--2H are transverse cross-sectional views taken along line F--F,G--G and H--H respectively, through the proximal portion of thedeflectable tip of FIG. 2B;

FIG. 3 is an enlarged view of a hinge assembly at the distal end of thecatheter of FIG. 1, illustrating a split-tip configuration with a pairof cylindrical ablation segments;

FIG. 4 is an exploded view of the hinge assembly of FIG. 3;

FIG. 5 is an end view of the hinge assembly of FIG. 3;

FIG. 6 is an enlarged view of an alternative hinge assemblyincorporating an integrated central hinge element and semi-circularablation segments with substantially planar electrodes thereon;

FIG. 7 is an end view of the alternative hinge assembly of FIG. 6;

FIG. 8 is an exploded view of the hinge assembly of FIG. 6;

FIG. 9 is an enlarged view of the hinge assembly of FIG. 6,incorporating a plurality of metallic pad electrodes on the ablationsegments;

FIG. 10 is an enlarged view of one of the ablation segments of the hingeassembly of FIG. 9;

FIG. 11 is a cross-sectional view of one of the ablation segments of thehinge assembly of FIG. 6;

FIG. 12 is a cross-sectional view of one of the ablation segments of thehinge assembly of FIG. 3;

FIGS. 13A-13C are perspective views of another hinge assembly embodimentof the present invention, incorporating a central hinge;

FIGS. 14A and 14B illustrate the central hinge embodiment of FIGS.13A-13C in the collapsed configuration;

FIG. 15 illustrates yet another embodiment of the hinge assembly of thepresent invention;

FIGS. 16A and 16B illustrate another embodiment of the hinge assembly ofthe present invention;

FIG. 17 illustrates yet another embodiment of the hinge assembly of thepresent invention, incorporating a tilting "cantilever" hinge design;

FIG. 18A illustrates another embodiment of one of the arm segments ofthe catheter of FIG. 1 incorporating a fluid chamber for directing anionic solution between the electrodes and tissue at the target site;

FIG. 18B illustrates an electrode panel for the arm segment of FIG. 18A;

FIG. 18C is a longitudinal cross-section of one of the arm segments ofFIG. 18A taken along lines C--C;

FIGS. 19A and 19B illustrate another embodiment that incorporates a pairof flexible arms that form a Y-shaped distal end;

FIGS. 20 and 21 schematically illustrate a method of forming a lesion onthe left atrial side of the septum within the patient's heart;

FIG. 22 schematically illustrates a method of forming a lesion acrossthe mitral valve annulus of the patient's heart;

FIG. 23 illustrates an alternative electrode configuration according tothe present invention; and

FIG. 24 illustrates a flexible printed circuit for the electrodes ofFIG. 23.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

Referring to the drawings in detail, wherein like numerals indicate likeelements, an electrophysiology catheter 2 is illustrated according tothe present invention. As shown in FIG. 1, catheter 2 generally includesa shaft 6 having a proximal end 18 and a distal end 22. Catheter 2includes a handle 4 secured to proximal end 18 of shaft, and adeflectable tip 28 coupled to distal end 22 of shaft 6. Deflectable tip28 comprises a movable ablation assembly 30 at its distal end thatgenerally includes a hinge assembly 32 and a pair of arms 34, 36 thatare movable between open (FIG. 3) and closed positions (FIG. 1). Aplurality of ablation or mapping electrodes 38 (see FIGS. 3-5) aremounted to arms 34, 36 for applying electrical energy to the patient, asdiscussed in further detail below. Handle 4 includes a tip actuationslide 10, a core wire torque ring 12 and a curvature adjustment slide11, as well as an electrical connector 14, all described more fullybelow.

FIGS. 2A and 2C-2E illustrate a distal portion 31 of deflectable tip 28,and FIGS. 2B and 2F-2H illustrate a proximal portion 33 of tip 28. Itshould be understood that the deflectable tip 28 illustrated in FIGS.2A-2H represents an exemplary embodiment, and the present invention isnot limited to this configuration. That is, the ablation assembliesdescribed below may be used with a wide variety of different tips andcatheters. As shown in FIGS. 2B and 2H, shaft 6 includes an axial lumen48 between its proximal and distal ends 18, 22. The preferredconstruction of shaft 6 includes a polyimide or ULTEM™ inner tube 50surrounded by an extruded topcoat 52 of a flexible polymer such asPEBAX™, urethane, etc. To add torsional and bending stiffness to shaft6, a braided reinforcement 54, usually stainless steel, may be embeddedin topcoat 52. As shown in FIG. 2H, inner tube 50 includes a number ofmanipulator and actuator wires, fluid channels, electrical conductorsand the like, extending from its proximal end to deflectable tip 28.Deflectable tip 28, in turn, defines at least five axial lumensextending from its proximal end to its distal end, all in communicationwith axial lumen 48 of inner tube 50.

In one embodiment, a stiffener or manipulator wire 66 for selectivelyadjusting the curvature of deflectable tip 28 extends through shaft 6into tip 28 to a distal ball 67, which is mounted to an anchor member 69near the distal end of tip 28 (see FIGS. 2A and 2D, discussed in furtherdetail below). As shown in FIG. 2D, manipulator wire 66 extends througha first axial lumen 55 in tip 28. When the catheter 2 has beenpositioned in the heart, the configuration of the deflectable tip 28 canbe selectively adjusted to impart the desired curvature and shape to thedeflectable tip as appropriate for the size and location of the area tobe mapped and/or ablated. In one embodiment, manipulator wire 66, whenadvanced into tip 28, will give tip 28 and manipulator wire 66 acombined bending stiffness greater than that of deflectable tip 28alone, but less than the bending stiffness of shaft 6. A more completedescription of this feature can be found in commonly assigned U.S. Pat.No. 5,487,757, the complete disclosure of which is incorporated hereinby reference.

As shown in FIGS. 2C-2G, second and third axial lumens 56, 57 within tip28 receive actuator wires 58, 59 for manipulating arms 34, 36 ofablation assembly 30 (see FIG. 3). Actuator wires 58, 59 extend to ayoke 78 of ablation assembly 30 for manipulating the arms 34, 36, asdiscussed in detail below. As shown in FIG. 2H, actuator wires 58, 59are joined into a single, common actuation member 61 within shaft 6 foractuation of both wires 58, 59 (and both ablation arms) substantiallysimultaneously. Of course, it will be recognized that the actuator wires58, 59 may remain separate through shaft 6 for independent actuation ofthe ablation segments. Deflectable tip 28 further includes a fourthaxial lumen 70 through which a core wire 72 extends. As shown in FIG.2D, core wire 72 forms a loop in anchor member 69 at or near distal endof tip 28 to enable rotational manipulation of tip 28. In a preferredembodiment, core wire 72 extends through shaft 6 and comprisesTEFLON®-coated stainless steel. Catheters utilizing such a core wireconstruction are disclosed in co-pending application Ser. No.07/866,383, the complete disclosure of which has previously beenincorporated herein by reference.

Referring again to FIGS. 2G and 2H, tip 28 further includes a fifth,central lumen 73 for receiving electrode wires 74, thermocouple wires 76(see FIG. 2H)) and a fluid tube 75. Of course, each of these componentsmay extend through separate lumens, rather than one, larger centrallumen 73. As shown in FIG. 2F, fluid tube 75 is preferably coupled to apair of fluid conduits 85, 87 extending through tip 28 to the ablationsegments for delivering fluid to each segment as discussed below. In anexemplary embodiment, fluid conduits 85, 87 are bonded to fluid tube 75with a fluid tight sheath 89 formed of a suitable material, such as aDacron™ mesh impregnated with a silicone adhesive. Each of electrodewires 74 is connected to one of the electrodes 38 (FIG. 3). In therepresentative embodiment, wires 74 are bundled together through shaft 6(see FIG. 2H) and then split apart into two flex circuits 77, 79 (FIG.2F), each extending to one of the ablation segments, as discussed below.As shown in FIG. 2G, flex circuits 77, 79 are joined to wires 74 at ajunction 81 within tip 28 having an insulating adhesive dome 83. Thethermocouple wires 76, typically copper and constantan, extend into anaperture (not shown) in arms 34, 36, where they are anchored with hightemperature adhesive.

Referring again to FIGS. 2A, 2C and 2D, yoke 78 includes an annularmounting portion 91 extending into tip 28, where it is attached toanchor member 69. Anchor member 69 is a substantially annular memberthat is coupled to the outer walls of tip 28 (see FIG. 2A). As shown inFIG. 2D, anchor member 69 has a pair of cut-outs 93, 95 for receivingactuation wires 58, 59 and a number of holes for receiving manipulatorwire 66, central lumen 73 and core wire 72. Core wire 72 loops aroundthe distal end of anchor member 69 to form the core wire loop, therebyanchoring core wire 72 to tip 28. Accordingly, anchor member 69 includestwo holes 97 for receiving both portions of the core wire 72 loop.

Referring to FIGS. 3-5 and 12, one embodiment of the ablation assembly30 of the present invention will be described in further detail. Asshown in FIG. 3, ablation assembly 30 includes a hinge assembly 32coupled to the distal end of deflectable tip 28, and a pair of shaftsegments or arms 34, 36 pivotally mounted to hinge assembly 32.Specifically, hinge assembly 32 includes a yoke 78, a pair of hinges 80,82 mechanically linked to yoke 78 and a pair of actuator wires 58, 59coupled to hinges 80, 82. Hinges 80, 82 preferably comprise a relativelystrong metal, such as titanium, stainless steel, Nitinol™ or engineeringplastics, such as Ultem™. Actuator wires 58, 59 extend through thecatheter shaft to tip actuation slide 10 (FIG. 1) of handle 4 formechanically opening and closing arms 34, 36 (discussed below). Arms 34,36 will usually be configured to move between a closed position (dottedlines in FIG. 1) substantially parallel to the longitudinal axis ofshaft 6 and an open position having an included angle of about 1 to 270degrees in the expanded position, preferably about 90 to 180 degrees andmore preferably between about 120 to 175 degrees. This latterconfiguration causes a spring-like contact at the ends of the ablationarms to facilitate the application of axial force by the catheter shaftagainst the arms. The actual application of arms 34, 36 to theirregularities of the surface of the interior of the heart will probablybe most extensive (and effective) with an included angle of less than150 degrees.

Once arms 34, 36 have been expanded and positioned in engagement withthe heart tissue, catheter shaft 6, 28 will be used to apply an axialforce against arms 34, 36 to maintain continuous contact pressureagainst the tissue. As those skilled in the art will appreciate,catheter shaft 6, 28 can be manipulated to apply a centralized,symmetric and evenly balanced axial force against arms 34, 36, whichallows a relatively long area of tissue to be engaged by two shortersegments (i.e., arms 34, 36). In addition, the arms 34, 36 provideincreased and evenly distributed contact pressure across the entirelength of the desired ablation location. Actuator wires 58, 59 closearms 34, 36 against the tissue, which enhances the contact therebetween.In the preferred embodiment, proximal movement of actuator wires 58, 59(i.e., pulling on these wires) will close arms 34, 36, while distalmovement or pushing on wires 58, 59 will open arms 34, 36. However, itwill be recognized that arms 34, 36 may be actuated in the reversedirection.

Referring to FIG. 3, each arm 34, 36 will include a plurality ofablation electrodes 38 extending along the length of arms 34, 36 (notethat electrodes 38 are only schematically illustrated in the drawings).Preferably, ablation electrodes 38 are coils or solid rings that arespaced from each other along arms 34, 36 and include temperature sensors88, such as thermocouples or thermistors. The electrodes 38 andtemperature sensors 88 are electrically coupled to wires 74, 76 withinshaft 6 by individual insulated wires 90, 92, respectively (see FIG.12). However, they may also be electrically connected by flexibleconductors (not shown), such as flex circuits, silicon matrixmulti-filar ribbon cables, or the like. Flexible conductors have theadvantage that they will be more reliable during repeated flexion at thehinge points. Arm segments 34, 36 will be constructed to have adesirable stiffness, depending on the application. For example,relatively stiff arm segments 34, 36 could be useful in flatter areas ofthe atrium, while a softer construction would be more conformable tocurved (particularly convex) portions of the atrium. Softer armconstructions could be made to conform around a sharp bend in thecontact surface, such as the ostium of a vein or artery or a valveannulus. The length of arm segments 34, 36 will also vary depending uponthe number of electrodes 38 desired. Typically, each arm will includeone to three electrodes 38, which results in an arm length of about 1-3cm or an overall ablation length of 2-6 cm. However, it will be readilyrecognizable that the arms may be longer or shorter depending on theparticular procedure.

As shown in FIGS. 4 and 12, arm segments 34, 36 may have a circularcross-section, comprising a central mandrel core 94 attached, e.g.,glue, solder, weld, press-fit, or the like, at hinges 80, 82, and outersleeves 96 extending coaxially over mandrel cores 94. Core 94 and outersleeves 96 define an annular fluid passage 98 therebetween, which isfluidly coupled to a fluid lumen (not shown) within catheter shaft 6.Arms 34, 36 may include a plurality of holes along their length fordirecting coolant onto the target site. Alternatively, arms 34, 36 mayeach include a hole at their distal ends for allowing the coolant toflow through arms to convectively exchange heat with electrodes 38. Amore complete description of this method of cooling electrodes 38 can befound in commonly assigned, co-pending application "Fluid CooledAblation Catheter and Method for Making" U.S. Pat. No. 5,913,854(attorney docket no. 14875-003400), Serial No. unassigned, filedconcurrently with the present application, the complete disclosure ofwhich has previously been incorporated herein by reference.

As shown in FIGS. 2-5, the curvature imparted to deflectable tip 28 maybe selectively adjusted by axially translating manipulator wire 66within the catheter shaft 6. Preferably, the curve control allowsorientation of deflectable tip 28 between 0-270° of curve, morepreferably between 0-180°. Catheter 2 may include another control wire(not shown) extending to yoke 78 for rotating ablation assembly 30 bytwisting deflectable tip 28 relative to shaft 6. Typically, this controlwire is a tapered core wire which can be rotated to cause slighttwisting of the main catheter shaft 6, thereby allowing the angularorientation of the open hinge arms 34, 36 to be varied relative to shaft6. This allows the operator to rotate the position of arms 34, 36without physically rotating the entire catheter shaft 6, which providesfor finer control of this manipulation. When the distal shaft is curved,rotation of the tapered core wire causes lateral movement of the entiredistal array.

In a method according to the present invention, catheter 2 istransluminally, thoracoscopically (e.g., through an intercostalpenetration), and/or directly delivered into the thoracic cavity so thatdeflectable tip 28 is positioned adjacent the heart. An axial force maybe applied to manipulator wire 66 by sliding adjustment slide 11 toadjust the curvature of tip 28. When the desired degree of curvature hasbeen obtained, deflectable tip 28 may be further positioned rotationallyby rotating torque ring 42, thereby exerting torque on core wire 42 oran additional control wire (not shown) which rotates the deflectable tipabout the longitudinal axis. When ablation assembly 30 has beenpositioned near a desired target site, actuator wires 58, 59 are moveddistally to pivot arms 34, 36 about hinges 80, 82, preferably until arms34, 36 are positioned transverse to the shaft axis. Catheter 2 can thenbe moved distally (or proximally) to engage the heart tissue at thetarget site with arms 34, 36. Catheter shaft 6 will exert an axial forceagainst arms 34, 36, and tensioning or pulling of wires 58, 59 willenhance the contact of arms 34, 36 against the heart tissue to maintainuniform contact pressure with the tissue. Radiofrequency current is thendelivered through connector 46 and electrode wires 74 to electrodes 38,through which current is conducted to the heart tissue to performablation. Mapping may also be accomplished when catheter 2 is used withan ECG.

The present invention is not limited to the hinge assembly describedabove and shown in FIGS. 3-5. For example, an alternative ball andsocket hinge design is illustrated in FIGS. 15, 16A and 16B. As shown inFIG. 15, ablation assembly 30' includes a ball and socket rotationallinkage 250 pivotally coupled to a pair of arm segments 252, 254. Aplurality of ablation or mapping electrodes 255 are disposed on each armsegment 252, 254 as described above. Arms segments 252, 254 may have asemi-circular cross-sectional shape (FIG. 15), or a cylindrical shape(FIGS. 16A and 16B). Each arm 252, 254 is movably coupled to deflectabletip 28 by a curved support wire or shaft 256, 258, respectively. Supportwires 256, 258 extend from arms 252, 254 into slits 260 in deflectabletip 28, where they are coupled to actuator wires 58, 59 for pivotingarms 252, 254 about linkage 250. In use, arms 252, 254 may be pivotedbetween a closed position (not shown) on either side of, andsubstantially parallel to, tip 28, and an open position (FIG. 15)transverse to tip 28. In the open position, support wires 256, 258support arms to facilitate their engagement with the patient's tissue.

FIGS. 6-10 illustrate another embodiment of a distal ablation assemblyfor use with catheter 2 according to the present invention. Similar tothe previous design, ablation assembly 100 includes first and second armsegments 108, 110 pivotally coupled to a central hinge member 102. Asshown in FIG. 8, central hinge member 102 includes a pair oflongitudinal support members 109, 111 each having an integral hinge 116,118. Support members 109, 111 can be designed (as shown) with a recessor plenum 123 for delivery of fluid under and to the electrodes 122mounted on top (see FIGS. 9 and 10). Mounting/cover plates 126 cover theplenum channels 123 and provide surface for mounting electrodes 122 (asshown in FIG. 9). Cover plates 126 may have holes for passing fluid toor through the electrodes 122 mounted thereto (not shown). A centralline channel 125 provides a conduit for running electrical wires and/orthermocouples to the electrodes 122. In this embodiment, arm segments108, 110 have a semi-circular cross-sectional shape (see FIG. 11), andare preferably formed using a silicone liquid injection molding (LIM)technique to mold-form arm segments 108, 110 around support members 109,111. As shown, ablation assembly 100 further includes a yoke 114 and apair of actuator wires 104, 106 for pivotally coupling arms 108, 110 andsupport members 109, 111 to catheter shaft 6 (FIG. 1). Hinges 116, 118are preferably offset from the yoke 114 axis so that hinges 116, 118 canbe disposed adjacent each other (FIG. 6). Hinges 116, 118 are designedto minimize interference with the planar contact of cover plates 126with the tissue (i.e., hinges 116, 118 do not protrude outward when armsegments 108, 110 are open).

Arm segments 108, 110 each include a plurality of electrodes 122disposed on cover plates 126. In one configuration, electrodes 122 havea flattened coil design (not shown) to provide a relatively flexibleelectrode length. In another configuration, electrodes 122 each comprisea metallic pad 124 mechanically or adhesively attached to cover plate126 (FIG. 9), or in an alternative configuration, to an underlyingflexible printed circuit 128 (FIG. 10). Flexible printed circuits 128provide a reliable electrical connection from electrodes 124, around thehinge joint 102, to connection wires 74 in shaft 6 (see FIGS. 2A-2C). Inaddition, flexible printed circuits 128 may include a thermocouplejunction (not shown) across several layers in the circuit for providingtemperature sensing. As shown in FIG. 8, electrode pads 124 arepreferably relatively thick (i.e., on the order of about 0.005 to 0.020inch), and include notches 130 that provide mechanical bending points toincrease flexibility of pads 124. Alternatively, electrode pads 124 maycomprise a thin film on the order of about 0.0001 to 0.005 inch thick,or a flexible grid or mesh arrangement (see FIGS. 18A and 18B).

As shown in FIG. 11, arm segments 108, 110 each include a fluid channelthrough recesses 123 of support members 109, 111, which are preferablymade of a suitable thermoplastic material, such as ULTEM™ or metal. Thefluid channels or recesses 123 are coupled to a fluid lumen (not shown)in catheter shaft 6 for allowing fluid coolant to exchange heat withelectrodes 122 and/or to bathe the tissue at the target tissue. As inthe previous embodiments, arms 108, 110 may include a plurality of holesfor directing the fluid onto the target tissue, or end holes forallowing convective cooling of electrodes 122. Arms 108, 110 alsoinclude thermocouples 134 adjacent to electrodes 122 for providingtemperature sensing.

Referring now to FIGS. 18A-18C, another embodiment of the ablationassembly will now be described. As shown in FIG. 18A, ablation armsegments 250 preferably have a semicircular cross-sectional shape with arelatively planar contact surface 252 on one side of the arm segment250. Similar to the previous embodiment, each arm segment 250 willinclude a fluid plenum 132 (FIG. 18C) coupled to one of the fluidconduits 75, 73 within deflectable tip 28 for delivering fluid to thetissue at the target site. In this embodiment, a flexible circuit 254 ismounted within each arm segment 250. Flexible circuit 254 has one ormore electrodes 255 mounted on it with a plurality of openings 256 forfluidly coupling the fluid channel 132 with cavities 258 within armsegment 250. Recessed cavities 258 each provide an interface volume offluid between electrodes 255 and the target site. In addition, recessedcavity 258 serves to distance the electrodes 255, preferably by about0.25 to 1.5 mm, to minimize or completely prevent direct contact betweenthe electrodes 255 and the tissue.

The fluid delivered into cavities 258 will preferably be an ionicsolution, such as isotonic saline, that conducts electrical current soas to carry the RF ablation energy from electrodes 254 to the tissue.Thus, a fluid interface is created between the electrodes 255 and thetissue to minimize direct contact between electrodes 255 and the tissueand surrounding blood. The fluid interface minimizes overheating andcoagulation of the blood, and damage to the tissue. This effectivelyeliminates the need to remove the catheter and clean the tip after aseries of lesions have been formed with the ablation segments 250.

Of course, it should be recognized that this concept of creating a fluidinterface between the electrodes and the tissue is not limited to thesplit tip catheter embodiments described above. For example, thecatheter assembly may include a single rigid tip portion with a similarconstruction as one of the ablation arms shown in FIG. 18A.Alternatively, the catheter may include a flexible tip portion having aplurality of longitudinally extending slots or apertures formedtherethrough. In this embodiment, for example, the catheter may includean electrode or electrodes disposed within the distal tip portion of theshaft. The electrode may have holes aligned with the holes of the distaltip portion (which can be an insulating sheath) for allowing fluid to bedelivered through the holes to create an electronically conductive fluidinterface between the electrodes and the tissue. The fluid, such asisotonic saline, passing through the openings becomes energized withsufficient RF energy supplied by the electrodes to ablate the tissue. Amore complete description of this concept can be found in commonlyassigned, co-pending application Serial No. Unassigned, "Linear AblationCatheter", filed concurrently with this application now U.S. Pat. No.5,919,188, the complete disclosure of which has previously beenincorporated herein by reference.

Referring now to FIGS. 13A-13C and 14A-14B, another ablation assemblyincorporating a central hinge according to the present invention will bedescribed. As shown, ablation assembly 140 includes a pair of curvedflexible support arms 142, 144 extending from the distal end ofdeflectable tip 28. Support arms 142, 144 are coupled to, or integralwith, a linear ablation segment 146 that spans across support arms 142,144. Linear ablation segment 146 includes first and second movableportions 148, 150 and a central thinned section 152 which is attached toan actuation wire or mandrel 154 to form the hinge point for ablationsegment 146. Ablation segment 146 preferably includes a groove 151extending along its proximal surface for receiving portions of supportarms 142, 144. As can be appreciated, axial movement of wire 154, whichis suitably coupled to one or both actuator wires 58, 59, causespivoting of movable portions 148, 150 about thinned section 152.Specifically, withdrawing wire 154 into tip 28 causes the mid-portion ofablation segment 146 to collapse toward the center until movableportions 148, 150 meet along their length in the middle (see FIGS. 14Aand 14B). In this manner, ablation segment 146 can be moved from aclosed or delivery position (FIG. 14A), in which movable portions 148,150 are close together and generally parallel to tip 28, and an open orexpanded position (FIG. 13A), in which movable portions 148, 150 foldout to form linear ablation segment 146 having a generally planarcontact surface 156 perpendicular to the shaft axis.

As shown in FIG. 13A, a plurality of electrode pads 160 are disposed oncontact surface 154 of ablation segment 146. Preferably, electrode pads160 and the various electrical/temperature sensor wires (not shown) aresnapped into ablation segment 146, which is constructed from a suitablethermoplastic material. Alternatively, the electrodes, sensors and wiresmay be injection molded into segment 146. The electrical wires extendthrough the curved lateral support arms 142, 144 of ablation segment 146to deflectable tip 28 and catheter shaft 6. Similar to previousembodiments, ablation segment 146 may include a fluid channel (notshown) for directing coolant fluid through segment 146 to cool electrodepads 160 and tissue at the target site. The fluid may exit throughmultiple holes (not shown) in planar surface 154, or through exit holesat the ends of movable portions 148, 150. In the latter configuration,the coolant acts as a heat exchanger, rather than bathing the tissueinterface. The fluid is delivered from the catheter shaft to eachablation segment 148, 150 through the support arms 142, 144.

FIGS. 19A and 19B illustrate a modified design of the central hingeassembly illustrated in FIGS. 13 and 14. As shown, catheter shaft 6 hasa bifurcated distal end that includes a pair of arms 170, 172 extendingaway from each other to form a Y-shaped distal end. Arms 170, 172 arepreferably biased away from each other into the configuration shown inFIG. 19B, i.e., with arms 170, 172 defining an included angle of about45 to 90 degrees. Catheter 2 may further include a sleeve (not shown) tourge arms 170, 172 into a parallel configuration for delivery to thetarget site. Arms 170, 172 are flexible enough to allow pivoting about acentral living hinge 174 at their connection point with shaft 6. In thisway, the surgeon can push arms 170, 172 against the heart tissue to movethem into an open position, preferably defining an included angle ofabout 120 to 170 degrees, as shown in FIG. 19B. The natural biasing ofarms toward the open configuration will facilitate uniform contact withthe heart tissue. The arms would be collapsed into a parallelorientation with shaft 6 for removal by pulling back into a deliverysheath (not shown).

FIG. 17 illustrates another embodiment of ablation assembly according tothe present invention. As shown, ablation assembly 200 includes a curvedsupport arm 204 and a manipulator member 202, such as a wire or mandrel,extending from deflectable tip 28 to a single, continuous linearablation segment 206. In this embodiment, ablation segment 206 is acontinuous member that does not collapse or fold onto itself as inprevious embodiments. A plurality of electrodes 210 are coupled toablation segment 206 as described above. Electrodes 210 may be rings,coils, metallic pads, flattened coils, or any other suitable design.Ablation segment 206 is coupled to actuator wire 58 (FIGS. 2A-2C, onlyone actuator wire is required in this embodiment) for rotating ablationsegment 206 between a delivery position, substantially parallel todeflectable tip 28, and a contact position (FIG. 17) substantiallyperpendicular to tip 28, where support arm 204 provides the pivot point.In this embodiment, deflectable tip 28 includes a longitudinal opening208 for receiving ablation segment 206 as it rotates into the deliveryposition. Thus, proximal retraction of manipulator member 202 causesablation segment 206 to rotate into opening 208.

Alternatively, retraction of both shafts 202, 204 may withdraw segment206 into deflectable tip 28. Similarly, distal movement or pushing orshaft 202 causes segment 206 to rotate into the perpendicular or contactposition shown in FIG. 17. At this point, a central, symmetric forcedelivered through catheter shaft 28 on segment 206 maintains a uniformcontinuous contact with the tissue.

FIGS. 20, 21 and 22 illustrate exemplary methods of creating asubstantially linear lesion in the left atrium of the heart according tothe present invention. Creating a lesion in this portion of thepatient's heart may be desirable, for example, in a catheter ablationprocedure similar to the surgical Maze procedure for treating atrialfibrillation or flutter. This procedure typically involves ablating longlinear incisions through the heart wall to electrically partitionportions of the heart. Ablation arms 34, 36 are collapsed together forpercutaneous introduction into the patients vasculature. As shown inFIGS. 20 and 21, ablation arms 34, 36 are endoluminally delivered intothe right atrium through the inferior vena cava, and then delivered intothe left atrium through a transseptal puncture 300. Once arms 34, 36 arepositioned within the left atrium, actuator wires 58, 59 are pulled (orpushed) to open arms 34, 36 as shown in FIGS. 20 and 21. The catheter 2can then be pushed forward into contact with tissue between the ostia ofpulmonary veins (FIG. 20). Alternatively, the catheter can be retractedproximally so that the arms 34, 36 press against the septum, as shown inFIG. 21. It should be noted that the procedure shown in FIG. 21 willpreferably be accomplished with circumferential electrodes, such asthose shown in FIGS. 3-5, or electrodes mounted to the "backside" of theablation arms (i.e., the opposite side as that shown in FIGS. 6-10 and18). Alternatively, a catheter having an ablation assembly as shown inFIGS. 6-10 or 18 may be introduced retrogradely into the left atriumthrough the aorta via the left ventricle, and then pushed against thedesired left atrial location (FIG. 22).

FIG. 22 illustrates another method of using the present invention tomake a linear lesion at the ostium of a pulmonary vein or between thepulmonary veins and mitral annulus. As shown, tip 28 of catheter 2 isadvanced in retrograde fashion through the arterial system, across theaortic valve, and into the left atrium via the left ventricle. One orboth arms 34, 36 are spread open by suitably manipulating actuator wires58, 59, and the catheter is advanced so that one of the arms 34, 36cannulates the pulmonary vein and the other arm contacts the atrial walladjacent the mitral annulus. Alternatively, the arms 34, 36 may beretracted against the mitral annulus to create a lesion between thepulmonary vein and the mitral annulus with the backside of theelectrodes. Similar to the above method, the electrodes in thisembodiment will either be circumferential, or mounted to the backside ofthe arms.

FIGS. 23 and 24 illustrates an alternative electrode configuration forone of the ablation segments described above. In this configuration, anarray of discrete block electrodes 260 are disposed on an electrodesupport plate 262. As shown, block electrodes 260 are spaced from eachother, and oriented such that grooves 264 formed within the electrodes260 extend along different directions from each other. As shown in FIG.24, annular flexible circuit traces 266 extend underneath blockelectrodes 260 to couple the electrodes to the connectors within thecatheter shaft (not shown), as described above. Annular flexible circuittraces 266 preferably have an open interior space 268 to allow fluidflow through electrode blocks 260 to the tissue interface.

What is claimed is:
 1. An apparatus for recording electrical signalsand/or for applying energy to a target site within a patientcomprising:a shaft having distal and proximal end portions and alongitudinal axis therebetween; an ablation segment at the distal endportion of the shaft defining first and second opposing ends and havingone or more electrodes disposed therebetween; a connector extendingthrough the shaft for electrically coupling the one or more electrodesto a source of electrical energy; a force element coupled to the shaftand disposed to apply an axially directed force to the ablation segmentbetween the first and second opposing ends, and the ablation segmentcomprising a substantially linear arm movable between a collapsedposition sized for delivery through a percutaneous penetration in thepatient and an expanded position substantially perpendicular to theshaft axis at which the ablation segment forms a substantiallycontinuous surface transverse to the longitudinal axis of the shaft forcontacting tissue at the target site.
 2. The apparatus of claim 1wherein the source of electrical energy is a Radiofrequency generator.3. The apparatus of claim 1 wherein the distal end portion of the shafthas a curvature, the apparatus further comprising an actuator coupled tothe proximal end of the shaft for adjusting said curvature.
 4. Theapparatus of claim 1 further comprising an actuator coupled to theproximal end of the shaft for rotating the ablation segment about theshaft axis.
 5. The apparatus of claim 1 wherein the linear arm includesfirst and second arm segments and an integral hinge therebetween forcollapsing the arm segments about the integral hinge.
 6. The apparatusof claim 5 wherein the integral hinge is a living hinge, the armsegments being connected together by a thinner portion that allows thearm segments to pivot about the thinner portion.
 7. The apparatus ofclaim 1 wherein the linear arm is pivotable about an axis perpendicularto the shaft axis from a first position, in which the linear arm issubstantially parallel to the shaft axis, to a second position, in whichthe linear arm is substantially perpendicular to the shaft axis.
 8. Theapparatus of claim 1 wherein the electrodes are divided into multiplesegments to improve the flexibility of the electrodes along the ablationsegment.
 9. The apparatus of claim 1 further comprising one or moretemperature sensors coupled to the electrodes on the ablation segment.10. A steerable electrophysiology catheter comprising:a shaft having aproximal end, a distal end and an axial lumen therebetween; first andsecond ablation segments at the distal end of the shaft each having aplurality of electrodes disposed therebetween, a connector extendingthrough the shaft for electrically coupling the electrodes to a sourceof electrical energy; and one or more actuator elements extendingthrough the axial lumen of the shaft from the proximal end to the distalend, the actuator elements being coupled to the ablation segments forpivoting the ablation segments into an open position transverse to theshaft axis.
 11. The catheter of claim 10 wherein the actuator elementsare axially movable within the catheter shaft for pivoting the ablationsegments between the open position and a closed position, substantiallyparallel to the shaft axis.
 12. The catheter of claim 10 wherein thesource of electrical energy is a Radiofrequency generator.
 13. A methodfor applying energy to a target site in a patient's bodycomprising:moving a distal ablation segment of a catheter into anexpended position, the ablation segment having first and second ends andthe catheter defining a catheter axis, the ablation segment beingsubstantially transverse to the catheter shaft axis when in the expandedposition; the moving step being carried out by pivoting a single,substantially linear arm about a pivot axis perpendicular to thecatheter axis from a collapsed position, at which the arm issubstantially parallel to the catheter axis, to the expanded position,at which the linear arm is substantially perpendicular to the shaftaxis; contacting tissue at a target site with one or more electrodes onthe ablation segment; applying an axial force to the ablation segmentbetween the first and second ends of the ablation segment to maintaincontact pressure between the ablation segment and the tissue; andapplying energy to the one or more electrodes and to the tissue at thetarget site.
 14. The method of claim 13 further comprising:deliveringthe ablation segment through a percutaneous penetration in the patient;and endoluminally advancing the ablation segment to the target site. 15.The method of claim 13 further comprising:delivering the ablationsegment through an intercostal penetration in the patient into thethoracic cavity; and positioning the ablation segment adjacent thetarget site on the epicardium.
 16. An apparatus for applying electricalenergy to a target site on a patient comprising:a shaft having distaland proximal end portions and a longitudinal axis therebetween; asubstantially linear support arm disposed at the distal end portion ofthe shaft and having first and second ends and one or more electrodesdisposed thereon, the support arm being movable to form a substantiallycontinuous contact surface transverse to the longitudinal axis of theshaft; a connector extending through the shaft for electrically couplingthe electrodes to a source of electrical energy; and a force elementcoupled to the shaft and disposed to apply an axial force to the supportarm between the first and second ends.
 17. The apparatus of claim 16wherein the linear support arm comprises first and second arm segmentsand an integral hinge therebetween, the first and second arm segmentsbeing pivotable about the integral hinge from a collapsed configuration,in which the arm segments are disposed together, and an expandedconfiguration, in which the arm segments form a substantially continuousline transverse to the shaft axis.
 18. The apparatus of claim 16 whereinthe linear support arm is pivotable from a delivery configuration, inwhich the arm is substantially parallel to the shaft for endoluminaldelivery to the target site, to an expanded configuration, in which thearm forms a substantially continuous line transverse to the shaft axis.19. The apparatus of claim 18 wherein the distal end portion of theshaft defines a longitudinal opening for receiving a portion of thesupport arm in the delivery configuration.
 20. The apparatus of claim 18wherein the force element comprises first and second curved, flexiblesupport shafts extending from the distal end portion of the shaft to thesupport arm, the support shafts providing a distally directed forceagainst the arm between the first and second ends to maintain contactpressure between the electrodes and the tissue.
 21. The apparatus ofclaim 20 wherein one of the support shafts is axially movable forpivoting the support arm between the delivery and expandedconfigurations.